Effects of Steelmaking Slag Addition on Growth of Marine Phytoplankton

Abstract

Culture experiments of a natural phytoplankton assemblage collected from coastal surface water and a mono-specifically cultured diatom were conducted to investigate the possibility of steelmaking slags to use as a nutrient resource for marine phytoplankton. Two kinds of slags, a decarburization slag and a dephosphorous slag, were tested in batch cultures under freely drifting pH. Leaching experiment to determine dissolution of nutrient elements from the slags demonstrated that phosphate and reactive silicate are released into seawater, while rate of their dissolutions does not simply depend on amount of the slags. Excess addition of the slags (3 300 mg/l ) decreased phosphate in the seawater probably due to precipitation with calcium of main component of the slags. Growth of natural phytoplankton assemblage was evidently enhanced by addition of the slags at 33 mg/l. However, excess addition (3 300 mg/l ) suppressed the growth of phytoplankton due to not only decreased phosphate and silicate but also increased pH to 10. This shift to alkaline might decrease considerably solubility of iron (essential nutrient for phytoplankton growth), although organic ligands existed. These results indicate that slag enrichment would be effective at a lower dose to avoid pH increase. Although in our study 33 mg/l was confirmed to be the best dose, solubility of the elements and pH increase might be different with different slags. Therefore, the best dose should be determined for each slag before application.

Growth promotion effect of steelmaking slag onSpirulina platensis

“…Protein content increases should also be associated with iron dissolution. This idea is also supported by the increase in marine phytoplankton fluorescence intensity by iron from SMS (SMS diameter: 5-20 μm) [23]. Another explanation for the change in protein content is the pH increase.…”

Continuous Supply of Bioavailable Iron for Marine Diatoms from Steelmaking Slag

“…Haraguchi et al 29) also reported a similar pH increase with the addition of 33 mg L Ϫ1 of but with no growth inhibition. Therefore, the present condition did not negatively affect the growth of phytoplankton.…”

“…The fine grains also allow the elements to easily dissolve in culture media as reported previously. 25,26,28,29) …”

“…The fine grains also allow the elements to easily dissolve in culture media as reported previously. 25,26,28,29) Mo, 57 nmol L Ϫ1 Co and 10 nmol L Ϫ1 Se as trace elements chelated with approximately 15 mmol L Ϫ1 EDTA in artificial seawater. The culture was maintained in an exponential growth phase using sterile techniques to minimize bacterial contamination, while, the algal strains might not have been purely axenic.…”

Determination Method for Maximum Calcium Releasing Potential from Steel Slags, Marine Sands Alternatives in Seawater

“…10) Steel slag also can create reef-like habitat for fishes 11) and promote growth of some marine phytoplankton. 12) On the other hand, a large amount of calcium in the form of uncombined calcium called 'free lime' 13,14) can be dissolved into seawater or sediment from slag. However, with the application of slag to the marine environment, the free lime is easily transformed to calcium hydroxide through hydration reactions.…”